As Gary has pointed out, there are checkvalves to prevent drainback, and in systems lacking that, the positive displacement design of the oil pump prevents drainback. This essentially assures that oil is ready and waiting in the oil galleys of the head and crank journals to move as soon as pressure is developed by the pump. Full oil pressure is usually reached within just a few rotations of the engine actually firing.
The bottom line is that the delay in flow and pressure from not running to running is so miniscule as to be something you really don't have the opportunity to impact.
I.e., worry more about having the proper weight oil rather than driving on a cold motor. Motors are built to handle thermal shifts, but not oil that can't get to where it is needed.
I was always told to let it warm up for a few minutes because it can cause cracked heads if not. during high school my mom would go out and start my car like 5 minutes before I was ready to go. I never understood it, but whatever, she payed the gas bills then.
But now I get in, turn it on, wait for the RPMs to settle, then wait a few more seconds. Usually this takes 30-40 seconds in 10* weather. and obviously scrape windows if need be during this time. Then I just drive off slowly, trying to apply as little gas as possible (automatic). My tranny doesn't like to shift from 3rd to 4th very well if it's really cold, so I may get up to 2800 RPMs before it'll shift (have to get on a 65mph highway after about 4 minutes of residential). it usually takes until this point to reach operating temperature, or about 5 minutes. when warm it usually shifts at around 23-2500 RPMs with the way I accelerate.
I try to balance the line between idling too long and using fuel and allowing the engine to be ready. It may not be totally right, but it makes me feel better.